Although commercially available dryers have been provided to dewater sludge, it is difficult to dewater sludge sufficiently because the cellular micro-organism bodies that constitute the sludge develop the consistency of "glue" in an intermediate moisture range between the starting point of about 80% moisture and an acceptable moisture content of less than 50%. These cellular bodies consist of an outer "exoskeleton" lined with a membrane than contains the internal moisture. In order to properly dry such a sludge, the skeleton and membrane must be ruptured and the water therein released. However, if too many of the cells agglomerate before the material is dry enough, the material sticks together and does not dry sufficiently. Temperatures above approximately 160.degree. F. are required to provide sufficient vapor pressure (in a low pressure ambient) to rupture the cells.
Various methods have been disclosed in the prior art for dewatering sludge. For example, in U.S. Pat. Nos. 2,723,954 (Young) and No. 3,909,410 (Neukamm), a method of dewatering sludge using hot solid aggregate particles is disclosed. According to the methods of these patents, moist sludge is mixed with hot aggregate particles so that the sludge coats the particles and is dried. The sludge-coated aggregate particles are then subjected to mechanical stress to break away the coating from the aggregate particles. This forms dewatered sludge particles which are separated from the particles.
A method of dewatering sludge using hot oil is also disclosed in U.S. Pat. No. 4,097,378 (St. Clair). According to this method, the water contained in combustible sludge is dried by adding recycled cool high boiling oil and heating the mixture by direct contact with steam. The oil sludge mixture then has some water separated off comprising the condensed steam and some original water from the sludge. The mixture is then heated again by adding hot oil so that additional water is evaporated off by reducing the pressure. The steam thus produced is used for the direct steam heating of the previous step. The pressure is then again reduced to evaporate off additional water vapor. Finally, the dewatered sludge containing the added oil can be burned as a fuel.
A method for the treatment of waste and the production of heat is disclosed in U.S. Pat. No. 4,203,376 (Hood). According to this method, a solid organic waste is composted, preferably in admixture with sewage sludge, and subsequently the composted waste is burned. The waste is preferably burned in a kiln for calcining an inorganic calcinable material.
A flash reactor unit for treating waste materials is also disclosed in U.S. Pat. No. 3,985,510 (Taylor). The flash reactor unit includes a reactor chamber in which a stream of hot, high velocity exhaust gases are introduced at the bottom thereof. Sanitary waste liquid is sprayed in the chamber at the top of the chamber. In addition, metallic waste objects, such as tin cans, are introduced into the chamber with the hot gases continuously circulating the metallic cans. The surfaces of the metallic objects thus form a reaction surface for vaporizing liquid waste.